1. Field of the Invention
The present invention relates to non-spherical or off-axis reflective mirrors, and more particularly to aspheric mirrors produced by the elastic deformation of a spheric mirror.
2. Description of the Prior Art
Conventional spherical mirrors are usually produced by grinding and lapping of glass or other suitable substrates. Non-spherical or off-axis mirror sections, such as ellipses, hyperbolas, parabolas, off-axis parabolas and torics, are difficult and expensive to fabricate. Mirrors or reflectors having toric sections represent the most difficult mirrors to fabricate and use due to the lack of an axis of rotational symmetry.
Optical replication techniques have reduced the difficulty of producing aspherical optical elements since replication techniques require the production of only a single high quality master by polishing and lapping techniques. The master may then be replicated at substantially reduced cost and in large quantity. Toric elements remain difficult to produce, due to the difficulty in producing a high quality master, since both the base curvature and the cylindrical curvature must be accurately fabricated.
A toric mirror or reflector is defined as a reflector having two mutually perpendicular cylindrical surfaces with an X-axis radius of curvature R.sub.X and an orthogonal Y-axis radius of curvature R.sub.Y. A toric mirror surface can also be derived from the additive or subtractive combination of a spherical surface having a base radius o( curvature R.sub.C, where the cylindrical additive or subtractive differential radius lies along the X-axis and modifies the X-axis radius of curvature R.sub.CX.
Any toric mirror can be completely defined by the parameters R.sub.CX and R.sub.CY, where R.sub.CX represents the radius of curvature along the X-axis and R.sub.CY represents the radius of curvature along the Y-axis. One of these two parameters, typically R.sub.CY represents the base radius of curvature R.sub.C of the spherical component of the toric mirror while the second parameters, typically R.sub.CX, represents the modified radius of curvature which results from the cylindrical additive or subtractive component superimposed on the underlying spherical surface.
Using existing mirror fabrication techniques, it has been very difficult to fabricate an extremely high tolerance toric mirror surface at a cost enabling use in a mass produced product.